Multiple sipes and narrow grooves are often provided in the tread portion of a studless tire in order to improve braking performance on ice, especially at higher temperatures, i.e., near 0° C. (see, for example, Japanese Patent No. 3690836).
However, as disclosed in Japanese Patent No. 3690836, providing multiple sipes and narrow grooves in the tread portion divides the tread portion into multiple small sections, thereby potentially reducing the rigidity of the tread portion. This leads to the problem of difficulty in maintaining steering stability on snow, a type of performance that calls for high rigidity on the part of the tread portion.